Ch 2: The Cell

Goals:

•Anatomy of a typical cell

•Cell Membrane

•Discussion of internal structure of a cell with emphasis on the various organelles

Developed byJohn Gallagher, MS, DVM

1. Cells are the smallest living structure

2. Cell = functional unit of the body

3. Cytology = The Study of Cells

4. Ultrastructural Cytology = Cytology at the Electron Microscopic level

5. Histology = the study of tissues (next meeting)

Some Terminology:

Anatomy of a typical cell

1. Cell membrane

2. Cytoplasm= cytosol + organelles

3. Organelles

•Smallest: •Granule cell in cerebellum: 4 µ•RBC: 5-7 µ = 0.005-0.007 mm

•Largest: •Anterior horn cell in spinal cord: 135 µ •Ovum: 120 µ = 0.12 mm

•Longest: •Pseudounipolar cell (CNS to toe)

Fig. 2.1

Anatomy of a typical cell, cont’d

_ Shapes:– Squamous (scale) - flat,

capillaries, lungs– Cuboidal - lines ducts– Columnar - length > width,

digestive tract– Stratified - many layers– Many others will be covered in

histology (next two lectures)

Cell Membrane = phospholipid bilayer

_ Physical isolation of the cell contents from the environment (interstitium)

_ Regulation of exchange of materials with the environment

_ Sensitivity to changes in the environment

_ Structural support of the cell– Organelles, too!

Cell Membrane

Synonyms:•plasma membrane•plasmalemma•axolemma•others

Membrane permeability covered in physiology

Membrane Permeability

_ Diffusion– Concentration Gradient of Solutes

_ Osmosis– Water (solvent) through semipermeable membrane

_ Filtration– Hydrostatic Pressure

» Capillaries!_ Active Transport

– Requires energy (ATP)

Endocytosis = into the cell

_ Pinocytosis– Extracellular Fluid

_ Phagocytosis– Solid Objects, e.g., bacteria

_ Receptor-mediated Endocytosis– Special membrane proteins required

Exocytosis = out of the cell

_ Secretory vesicles (e.g. hormones)– Fluid and waste removal

Cytosol vs. cytoplasm

Cytosol = The thick fluid inside any cell

Often synonymous with cytoplasm (protoplasm) Cytoplasm = cytosol + organelles

Suspends organelles

Organelles

_ Structures INSIDE a cell that have specific functions wrt cellular structure, maintenance, or metabolism– Membranous

» Nucleus» Golgi apparatus» Endoplasmic reticulum» Mitochondria» Vesicles and lysosomes

– Nonmembranous» Ribosomes» Microtubules (cytoskeleton)» Actin/Myosin in muscle cells

Nucleus (= center)

_ Visible with LM_ Membrane bound

– Many pores_ DNA

– 23 Pairs of Chromosomes» Except gametes

_ Nucleolus– Most active DNA

Nucleus

Golgi Apparatus

•Packaging and shipping of proteins (secretory granules and transport vesicles)•Membrane renewal•Synthesis of Lysosomes

Fig 2.17

Exocytosis

Golgi Apparatus

Endoplasmic Reticulum

Synthesis, Storage, transport

Smooth ER Lipid synthesis

Rough ER Ribosomes make

it rough ER Protein synthesis

Mitochondrion / -a

•Energy Conversion for cellular activities

•Formation of ATP

•Double membrane

•Glycolysis and TCA cycle

•More prevalent in active cells, e.g., rods and cones

•Their own genome

•Self-replicating

Lysosomes

Ribosomes - RNA

60% RNA + 40% protein

Protein Factories

Fixed vs. free ribosomes

Cytoskeleton

4 major components:

1. Microfilaments (mostly actin)

2. Intermediate filaments

3. Microtubules (composed of tubulin subunits)

Function: support & movement of cellular structures & materials

Cilium – Cilia (pl.)

Compare to microvilli and flagella

In 9+2 array

Actin/Myosin

_ The contractile proteins in muscle cells_ Striations

Skeletal muscle

1. Gap Junctions2. Tight Junctions3. Desmosomes4. Basement Membrane

Intercellular AttachmentsChapter 4, pp 74-76

Fig 4-7

Act as:1. Seals betw cells2. Intercellular communication3. Added strength to resist

separation

Channel proteins (connexons) interlock and form pores

Abundant in cardiac and smooth muscle

Allows efficient intercellular communication

1) Gap Junctions

2) Tight Junctions

Interlocking membrane proteins

Found near surface of cells lining the digestive tract. Explain!

Adhesive Belt Junctions deep to tight junctions reinforce the seal

3) DesmosomesProteoglycan layer reinforced by transmembrane proteins (cell

adhesion molecules or CAMs)

Belt, button and hemidesmosomes

Found in superficial layers of skin

4) Basement Membrane

_ Reticular fibers + Basal Lamina_ Between epithelium and deeper

connective tissue_ Acts as a filter, and helps

epithelial regeneration

Fig 2.19 a

Mitosis (vs. meiosis)

_ Cell Division– Interphase – Between mitosis – Prophase – Chromosomes become bunched– Metaphase – Chromosomes gather at equator– Anaphase – Chromosomes move to poles– Telophase – The two new nuclei form– Cytokinesis – Actual cell separation– Two new diploid cells

Mitosis

Some cells

Fat cells (adipocytes) Cartilage cells (chondrocytes)

More cells

Neutrophil Plasma cell

Still more cells

Columnar cells Sperm cells (spermatozoa)

River Cullenagh, Ennistymon, Co Clare, Ireland